Question

您好我已经创建了以下代码来填充spinner，其中包含SQLite数据库中存储的表的第1列中的数据列表。当我运行程序时，旋转器上没有任何内容。我已粘贴下面的代码。如果有人可以帮助我解决那个值得高度赞赏的问题。

public class MainActivity extends ActionBarActivity implements AdapterView.OnItemSelectedListener {
    DatabaseHelper myDb;
    Spinner group;
    Spinner volt1;
    Spinner sf;
    Spinner energy;
    String group_text;
    String sf_text;
    String energy_text;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myDb = new DatabaseHelper(this);

        volt1 = (Spinner) findViewById(R.id.spinner_voltage);

        List<String>names = myDb.getAllNames();
        ArrayAdapter<String> adaptervolt = new ArrayAdapter<String>(this, R.layout.spinner_layout, R.id.txt, names);
        adaptervolt.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        volt1.setAdapter(adaptervolt);
    }

public class DatabaseHelper extends SQLiteOpenHelper {

    public static final String TABLE_NAME2 = "Spark Energy Table";

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    public List<String> getAllNames() {
        List<String> names = new ArrayList<String>();
        SQLiteDatabase db = this.getReadableDatabase();
        String selectQuery = "SELECT * FROM"+ TABLE_NAME2;

        db.beginTransaction();
        try {
            Cursor cursor_volt = db.rawQuery(selectQuery, null);
            if (cursor_volt.moveToFirst()) { 
                do {
                    names.add(cursor_volt.getString(0));
                } while (cursor_volt.moveToNext());
                cursor_volt.close();
            }

            db.setTransactionSuccessful();
        } catch (SQLiteException e) {
            e.printStackTrace();
        } finally {
            db.endTransaction();
            db.close();
        }
        return names;
    }
}

Xml文件1：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:weightSum="1">

    <TextView
        android:id="@+id/txt"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
</LinearLayout>

Xml文件2：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"    
    android:layout_width="match_parent"
    android:layout_height="match_parent"   
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"  
    tools:context=".MainActivity"
    android:id="@+id/id1">

    <Spinner
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:id="@+id/spinner_voltage"      
        android:layout_alignTop="@+id/textView2"
        android:layout_toRightOf="@+id/textView2"
        android:layout_toEndOf="@+id/textView2" />
</RelativeLayout>

Answer 1

您还没有在助手类中创建数据库。首先在你帮助类的oncreate方法中创建你的数据库。

您需要执行create语句来创建表和列。

尝试本教程寻求帮助 sqlite tutorial

使用sqlite数据填充微调器

1 个答案: